1. Technical Field
The present invention relates to a coordinate measuring machine having a vertically suspended probe which is movable vertically to engage and measure a part. The apparatus disclosed in this invention is a vertical motion lock and fine feed which may have use in other systems in which a light weight, accurately positioned member is to be moved precisely without backlash, yet with minimal inertial or other forces.
2. Background Art
Many coordinate measuring machines are known. Typically, such machines include a horizontally movable carriage including a vertical probe shaft and probe suspended from a cantilevered arm or bridge mechanism. The vertically suspended probe shaft is counterbalanced to be easily movable upward or downward as necessary to allow the probe to engage a part therebelow and allow a measurement of features on such part.
In such coordinate measuring machines, precise incremental vertical movement of the shaft is desirable with little or no backlash and with as little influence as possible on the position of the probe, its relationship to guide bearings and on the probe shaft geometry itself. Accordingly, it is desirable to have a fine feed mechanism which applies a minimum amount of force and torque consistent with desired movement and minimal backlash movement of either the probe shaft or the control mechanism without concurrent movement of the other.
Additionally, it is desirable to have a mechanism for selectively coupling and decoupling the probe shaft movement apparatus from the probe shaft as desired.
The prior art coordinate measuring machines do not have a suitable lock and fine feed mechanism for the vertical direction. The prior art has suggested several lock and fine feed mechanisms which are appropriate and highly desirable for horizontal movement of the carriage and a cantilever arm or bridge assembly, but such systems are not readily adaptable to a vertically suspended probe and the vertical movement thereof. The delicate balance between a counterbalance system and the force of gravity, together with rather delicate and high accuracy guide bearings and critical shaft geometry, with the concurrent requirements for high stiffness, low weight and a rigid structure, make a vertical fine feed and lock mechanism for a coordinate measuring machine difficult to attain.
Since many coordinate measuring machines are designed for use in an automatic mode wherein servo motors provide a controlled drive of the mechanical structure independent of human operators, a measuring machine advantageously should include a system for releasably moving the components in each of the desired directions, preferably including a fine feed for precise positioning in each direction.
U.S. Pat. No. 3,403,448 to W. F. Aller and owned by the assignee of the present invention illustrates generally a prior art cantilevered arm coordinate measuring machine having a vertically suspended probe shaft which is movable in the vertical direction by the operator's grasping the shaft and "man-handling" it into the desired position. U.S. Pat. No. 3,774,311 to Stemple illustates a bearing structure for movably mounting the probe for vertical movement with pairs of spool-type bearings providing guides for vertical movement of the probe along a generally predetermined path.
U.S. Pat. No. 3,817,111 illustrates a lock and fine feed mechanism for a coordinate measuring machine to effect or prevent movement in a generally horizontal plane. In such a system, a remote knob controls gripping of a threaded rod by a carriage mounted member which, when rotated while the rod is gripped, effects horizontal movement of the carriage with respect to a base.
U.S. Pat. No. 3,818,596 to Stemple and Allen discloses a variable torque magnetic particle clutch mechanically coupled to counterbalance and drive a probe vertically.
U.S. Pat. No. 4,207,680 to Bell and Tuss discloses an air counterbalance system for a vertical probe coordinate measuring machine in which an air cylinder is mechanically coupled to support a vertical probe which is mechanically moveable by an operator's directly grasping the probe and moving it.
U.S. Pat. No. 4,213,244 to Bell and Tuss also discloses a failsafe system for vertically mounted probes, in which movable brake members are mounted adjacent to the probe shaft and selectively engage the shaft to prevent its downward motion, e.g., if the counterbalance fails or the downward speed exceeds a predetermined rate.
Accordingly, the prior art coordinate measuring machines lack a vertical fine feed and lock mechanism for probe movement without imposing undesirable forces on the shaft or its mounting system.